Ojuela

I had a passing interest in the Mina Ojuela for some years, and have now become some what more manic on the local.I recently purchased a specimen as conichalcite, but the spec I have from some time ago, has bright apple green xls with quartz on the usual geothite matrix.On the 'new' spec I appear to have two minerals.Are thay both conichalcite? (the light green on dark green)

Hi UweYes I could do such tests, but I belive I am useing this section as it was intended, with pictures. (ie so those with a knowlege of mine/quarry/ outcrop from a particular local can give a pointer to the minerals possible present). There must be some one out there that has a good knowlelge of Mina Ojuela minerals.

William sorry did not mean to belittle your goddes,Mine is the god of dyslexia

I have quite a few specimens from Mapimi. I'm no expert on the mines there, but have seen a few pieces from them.

The dark green could be either malachite or olivenite, with the former more likely than the latter.

I think Uwe has the right idea: People post photos, we look at them, then we suggest species you can check out through other-than-visual means. I don't care how familiar someone might be with materials from any given locality, they are NOT going to be able to site-identify them unless the minerals are rather unique. And at places like Mapimi, there are simply too many "look-alikes" to scratch one's head over. It's gonna take tests.

Add malachite and olivenite to your list of "likely suspects" - and dig out the kitchen kemistry set... :~}

Hi RobI've have looked at Panczer book, and I find its very sketchy.Barthite was shown by E.Fischer to be cuprian austinite in 1944.The latest info I have on the Ojuela unknown, is a high probabililty that it'scuproadamite ( cuprian adamite). Although I am finding it hard to convincemy self, the crystal form dose not seam right for this species.

It's also about time someone did a comprehensive artical on this mine, as you say one of the great mineral local's. Although we dont want to see silly Tsumeb prices on specimens.

Having a look at your picture it could be a few things. I tend to agree with Uwe that it could very well be olivinte because as you decrease Ca and pH olivinite forms in the solution with conichalcite and lammerite (see Oxide zone geochemisty Williams 2000). However conichalcite forms solid solution series with not only adamite but duftite as well as Pb redily replaces Ca. What you might find in fact is that the conichalcite might be plumbian (i have done analysis that shows this) or could even be a calcian duftite. From the picture the dark green looks very similar to aresendescloizite from the mine which i analyized to be calcian, cuprian (in an up and coming paper) so my suggestion would be calcian, cuprian arsendescloizite and possibly austinite/adamite (the light green looks more like austinite).

Hi StuartIt looks like I'am going to have to have this specimen, tested by xrd and quantitative stuff.Thanks again for the possibilitys, this now throws some confusion on other specimens I have from Mina Ojuela.Steve R

I must say i dont know many things on Ojuela minerals, but the assosiations in that mine, as well as this particular picture, are much the same as in the mines of Laurion in Greece, to which I am very familiar (I live 35 miles from there).

In Laurion there are very similar specimens, where the paler lime-green mineral is usually proved to be Duftite (calcian) or Pb-rich Conichalcite, on darker "plain" Conichalcite. Both species however are usually sold as Conichalcite and Duftite from the locality is largely overlooked.

Finally the paler mineral could easily be Austinite. The Adamite-Olivenite series - at least in Laurion - is usually visually distinguishable due to the more clealy defined crystal shape (not just "botryoidal") with evident prism terminations.

I have been faced many times with questions like yours. I have collected quite a bit at the Black Pine mine and environs in Montana, USA. Your photograph could easily be of a Black Pine specimen. Additionally, I have collected similar species in the Tintic District, Utah, USA, and at Gold Hill, also in Utah. I found some similar appearing material with Wickenburgite at the Potter-Cramer property in Arizona that upon analysis was found to be an admixture of two species, visually undistiguishable until they were 'probed (the first species with lower atomic weight had Pb,Cu,Ca,As,V and a trace of S, the second species had higher atomic weight with greater Pb and no Ca or S). Duftite-beta/Mottramite?

Additionally, I have substantial collections of similar appearing specimens from world-wide locales, such as Tsumeb, Caldbeck Fells, and Cornwall. I have a number of "conichalcites" from the Ojuela Mine as well. In my specimens from the Ojuela mine, the conichalcite is about the same color as the lighter green mineral in your photo, but the habit of my specimens is different, but that is not determinative. On my specimens, the second species is a lighter green, not darker, and proved to be cuprian Austinite--a mineral which is often colorless at other locales when it is not cuprian.

If I had to guess, I would say that the lighter green mineral was Balydonite, but if I really wanted to stick my neck out, I might venture Arsentsumebite (Beudantite, another arsenate/sulfate is noted from Mapami). Of course, it could be Conichalcite or Duftite, or some combination.

I don't agree that the darker mineral is definitely a second mineral. It crystallized earlier and looks a tad "dirty" in the photo. By dirty, I mean that the material might not be one thing, but a mixture--perhaps inclusions of the underlying matrix. My guess for an identity would include all of the above along with possible Olivenite.

My suggestion is to have a few grains analyzed, but not to be surprized if the analysis does not produce an identity that clearly fits into an ideal formula. That is what I have found with the many pieces of similar appearing material from around the world that I have submitted for analysis.

Just yesterday, I obtained a number of reference grade specimens from an old collection. There were quite a number of well-documented ore specimens dating as far back as the early 1930's. Among them was a specimen labeled Barthite, from the Ojuela Mine. It's appearence is simalar to the darker material in your photo. Along the broken edge, it can be seen that the material is a mixture--a darker green layer over lighter green. Barthite was found to be a mixture of conichalcite, the darker green outside, and austinite, in this case, cuprian, the ligher green inside.

Later, I will post a photo and have it analyzed. We can compare notes.

I have collected Ojuela pieces for a number of years and I have seen similar aggregates to yours. Did you try a quick touch of dilute HCl to see if the darker material was simply calcite over an earlier coating of conichalcite? I know this happens from time to time.

Another contact who may be able to help you would be Peter Megaw. I don't have his email address handy, but it is listed on the collectors page of www.wulfenite.com . He works mainly with Mexican minerals and has a good bit of knowledge about what can be found there.

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